It is known to place an optical element, in particular a reticle having a measurement scale, into an eyepiece of a microscope, which in turn is received in a viewing tube of the microscope. For example, U.S. Pat. No. 4,172,662 to Vogel describes an eyepiece for a microscope wherein the eyepiece includes a main eyepiece tube 7 and an extension tube 6 coaxially received by the main eyepiece tube 7. A reticle 1 is mounted within the extension tube 7 and includes both a length scale and an angle scale. In order to change reticles for different applications, the user must remove the eyepiece from the viewing tube of the microscope, pull the extension tube out of the main eyepiece tube, extract the reticle and insert a different reticle, reinsert the extension tube into the main eyepiece tube, and replace the eyepiece in the viewing tube of the microscope. This operation is time consuming and carries significant risk that the optical elements of the eyepiece, including the reticle, will be smudged by finger contact. Moreover, if the eyepiece is locked in place in the viewing tube to prevent loss and theft, then exchange of the reticle becomes impossible.
Thus, a need exists for an improvement that allows optical elements to be quickly and easily inserted into and removed from a viewing tube of a microscope.